4,2’:6’,4”- and 3,2’:6’,3”-Terpyridines: The Conflict between Well-Defined Vectorial Properties and Serendipity in the Assembly of 1D-, 2D- and 3D-Architectures

A comparative investigation of the coordination assemblies formed between Co(NCS)(2) and two monotopic 4,2’:6’,4’’-terpyridine (4,2’:6’,4”-tpy) ligands or two related ditopic ligands is reported. Crystals were grown by layering MeOH solutions of Co(NCS)(2) over a CHCl(3) or 1,2-C(6)H(4)Cl(2) solution of the respective ligand at room temperature. With 4’-(2-methylpyrimidin-5-yl)-4,2’:6’,4”-terpyridine (6), the 1D-coordination polymer {[Co(2)(NCS)(4)(MeOH)(4)(6)(2)]∙2MeOH∙8H(2)O}(n) assembles with 6 coordinating only through the outer N-donors of the 4,2’:6’,4”-tpy unit; coordination by the MeOH solvent blocks two cobalt coordination sites preventing propagation in a higher-dimensional network. A combination of Co(NCS)(2) and 1-(4,2‘:6’,4”-terpyridin-4’-yl)ferrocene (7) leads to {[Co(NCS)(2)(7)(2)]∙4CHCl(3)}(n) which contains a (4,4) net; the 2D-sheets associate through π-stacking interactions between ferrocenyl and pyridyl units. A 3D-framework is achieved through use of the ditopic ligand 1,4-bis((n)propoxy)-2,5-bis(4,2’:6’,4”-terpyridin-4’-yl)benzene (8) which acts as a 4-connecting node in {[Co(NCS)(2)(8)(2)]∙2C(6)H(4)Cl(2)}(n); the combination of metal and ligand planar 4-connecting nodes results in a {6(5).8} cds net. For a comparison with the coordinating abilities of the previously reported 1,4-bis((n)octoxy)-2,5-bis(4,2’:6’,4”-terpyridin-4’-yl)benzene (3), a more flexible analogue 9 was prepared. {[Co(NCS)(2)(9)]∙2CHCl(3)}(n) contains a (4,4) net defined by both metal and ligand planar 4-connecting nodes. The (n)octoxy tails of 9 protrude from each side of the (4,4) net and thread through adjacent sheets; the arene-attached (n)octoxy chains associate through a combination of van der Waals and C–H...π interactions.